DESCRIPTION: The overall goal of this proposal is to further understand events in the Drosophila embryo that play a role in the modulation of screw (scw) activity and its spatial restriction to dorsal cells. Scw is a member of the TGF family whose RNA is uniformly localized, but its activity is not required in the ventral region. There are three models: (1) that scw and dorsally localized dpp form heterodimers that are necessary for dorsal structures; (2) that tolloid, a BMP-1 like metalloprotease that is dorsally localized, is necessary to process scw to its active form; and (3) that ventral short gastrulation prevents scw function. There are four aims. Specific Aim #1 centers on structure-function relationships in the scw protein. Specific Aim #2 addresses the possibility of scw involvement in later stages of development. Specific Aim #3 focuses on the establishment of molecular assays to test models for modulation of scw activity. Specific Aim #4 is to characterize scw biochemically.